Nickel base alloy

ABSTRACT

AN ALLOY CONSISTING ESSENTIALLY OF 12 TO 20% CHROMIUM, 13 TO 19% COBALT, 4.5 TO ABOUT 7% TITANIUM, 1.3 TO 3% ALUMINUM, 2 TO 3.5% MOLYBDENUM, 0.5 TO 2.5% TUNGSTEN, THE COMBINED MOLYBDENUM AND TUNGSTEN CONTENT BEING 3 TO 6%, 0.05 TO 0.15% CARBON, 0.005 TO 0.03% BORON, THE TITANIUM AND ALUMINUM CONTENT BEING BALANCED SO AS TO PROVIDE A TITANIUM RATIO WITHIN A SPECIFIED RELATIONSHIP AND A COMBINED TITANIUM AND ALUMINUM CONTENT OF 6.5 TO 9%, THE BALANCE OF THE ALLOY BEING ESSENTIALLY NICKEL WITH UP TO 0.75% MANGANESE, UP TO 0.2% YTTRIUM, UP TO 0.2% OTHER RATRE EARTH ELEMENTS SUCH AS CERIUM OR LANTHANUM AND UP TO 0.5% IRON.

June 6, 1972 w. J. BO'ESCH 3, 7,

NICKEL BASE ALLOY Filed may 5. 1970 5-Sheecs-Sheet 1 TITAN/UM, wr.

INVENTOR. WILLIAM J. BOESCH Wm Am Attorney June 6, 1972 w. J. BoEscH 3,667,938

mcxm BASE ALLOY Filed May 5. 1970 5 Sheets-Sheet 2 0; V) E k 80- A, P 40.7 (74 HRS.) a, P 4/.0 (1/3 HRS.) c, P 4/.6 (2/8 HRS.)

70 I I I l l LARSON MILLER PARAMETER P=T(20+L0gf)xl0-3 llO & I 30 k Q Q m V Q .90

o; t a Q 1 ea E 5' 70 so l/Vl E/V ro/a WEIGHT TUNGSTE/V 8055c EFFECT OF ruwasrsu mama/vs UPO/V m5 BY STRESS RUPTURE LIFE (6.0.Ti2.4A/) A A Attorney Jupe 6, 1972 w. J. BOESCH 3,667,938

NICKEL BASE ALLOY Filed May 5. 1 970 5 Sheets-Sheet 5 X-2563. o 60 Q 3: E 40 \l l0 I COBALT, WEIGHT EFFECT OF VARIATION IN COBALT UPON THE STRESS RUPTURE LIFE (/400F-92Ks1'} -o AVE. 0.0.95 CARBON I00- A ---A--- AVE. 0.044 CARBON 80- b 70- 2 so- =x-2492 50- ii x-2493 ,0 l I l BORON, ppm

EFFECT OF VA RM T/ONS IN CARBON AND BORON UPON THE STRESS RUPTURE LIFE (/400FI-92 Ksi) INVENTOR. WILLIAM J. BOESCH Z /MWL/PAQ/i WE Attorney June 6, 1972 w. J. BOESCH 3,667,938

NICKEL BASE ALLOY Filed May 5. 1970 5 Sheets-Sheet'd.

k I I I BLADE CYCLE 0 5 COMMERC/AL 2g 3.0- ALLOY A L BLADE CYCLE 0 K) E I t 4.0- I COMMERCIAL 2 ALLOY D g BLADE cYcLE \l 5.0- E o k 28/4 VA/VE CYCLE COMMERCIAL 8 ALLOY D VANE cYcLE I l l l l 0 40 80 I20 I60 200 240 TIME HOURS SULF/DAT/O/V EROS/0N TEST RESULTS FOR BLADE CYCLE KLOWEI? TEMPERATURE) AND VA/VE CYCLE (HIGHER TEMPERATURE) Fla 6 uv vE/v roe.

WILL/AM J. BOESCH UM LELA- A A Attorney June 6, 1972 W. J. BOESCH NICKEL BASE ALLOY 5 Sheets-Sheet 5 Filed May 5. 1970 Y XQQQQ q 3U QWSSGU QMQN INVENTOR. WILL/AM J BOES'CH A Horney United States Patent @fice 3,667,938 Patented June 6, 1972 Int. Cl. C22c 19/00 US. Cl. 75-171 6 Claims ABSTRACT OF THE DISCLOSURE An alloy consisting essentially of 12 to 20% chromium, 13 to 19% cobalt, 4.5 to about 7% titanium, 1.3 to 3% aluminum, 2 to 3.5 molybdenum, 0.5 to 2.5% tungsten, the combined molybdenum and tungsten content being 3 to 6%, 0.05 to 0.15% carbon, 0.005 to 0.03% boron, the titanium and aluminum content being balanced so as to provide a titanium to aluminum ratio within a specified relationship and a combined titanium and aluminum con tent of 6.5 to 9%, the balance of the alloy being essentially nickel with up to 0.75% manganese, up to 0.2% yttrium, up to 0.2% other rare earth elements such as cerium or lanthanum and up to 0.5% iron.

This application is a continuation-in-part of application Ser. No. 675,468 filed Oct. 16, 1967, now abandoned.

The present invention relates to high temperature alloys and more particularly to high temperature nickel-base alloys that exhibit an optimum combination of hot corrosion resistance, strength, creep resistance, phase stability and most importantly, stress rupture life.

Nickel-base alloys are known in the art that may be characterized by their resistance to hot corrosion, or by their high temperature strength or by their creep resistance and in some cases one of the above properties may be found in a particular alloy that also exhibits good phase stability when subjected to high temperatures for prolonged periods of time. However, the prior art is devoid of a single alloy which exhibits an optimum combination of hot corrosion resistance, strength, creep resistance and phase stability.

It is, therefore, an object of this invention to provide an alloy that exhibits such an optimum combination of properties.

It is a further object of this invention to provide a novel alloy having such an optimum combination of properties that can be produced commercially.

It is a more specific object of this invention to provide a novel alloy that can be commercially produced that exhibits an optimum combination of hot corrosion resistance, strength, creep resistance and phase stability when subjected to severe loads at elevated temperatures over extended periods of time.

Further objects and advantages will become apparent from the following description taken in conjunction with the drawings in which:

FIG. 1 is an isolife graph illustrating the effect of the titanium-aluminum relationship on rupture life,

FIG. 2 is a Larson-Miller diagram which compares rupture properties of prior art alloys with alloys of the invention,

FIG. 3 is a graph of the influence of tungsten on rupture life,

FIG. 4 is a graph showing how cobalt influences rupture life,

FIG. 5 is a graph illustrating the effect of variations in carbon and boron on rupture life,

FIG. 6 is a graphical representation of the sulfidationerosion test results of the invention alloy compared with two commercial alloys, and

FIG. 7 is a bar graph of sulfidation-erosion test results of the invention alloy compared with five commercial alloys.

Generally speaking the present invention contemplates an alloy having a composition within the limits, by weight, of 12 to 20% chromium, 13 to 19% cobalt, 4.5 to 7% titanium, 1.3 to 3% aluminum, preferably 2 to 3% aluminum, 2 to 3.5% molybdenum, 0.5 to 2.5% tungsten, the combined molybdenum and tungsten content being 3 to 6%, 0.05 to 0.15% carbon, 0.005 to 0.03% boron, the titanium and aluminum content being balanced so as to provide a titanium to aluminum ratio within a specified relationship (ABCD of FIG. 1), and a combined titanium and aluminum content of 6.5 to 9%, the balance of the alloy being essentially nickel with up to 0.75% manganese, up to 0.2% yttrium, up to 0.2% other rare earth elements such as cerium or lanthanum and up to 0.5% iron.

Within the foregoing limits of the alloy of the present invention the alloying components contained therein perform functions are related hereinafter.

The titanium content of the present invention is limited to an amount between 4.5 and 7% and the aluminum content is limited to an amount which provides a titanium to aluminum ratio within the area ABCD of FIG. 1, preferably between 2 and 3%. It is also necessary that in addition to the individual limits of the titanium and aluminum the total content of titanium plus aluminum be between 6.5% and 9.0%. The preferred ratio of titanium to aluminum is between 1.75:1 and 3.5:1.

The titanium and aluminum contents have been determined to be critical in several respects. It was discovered that as the titanium to aluminum ratio increases and/or as the total titanium plus aluminum content increases the strength of the alloy increases up to that percentage of these elements at which deleterious titanium or aluminum bearing phases occur as massive or eutectic gamma prime or eta on initial heat treatment. Formation of eutectic gamma prime is enhanced when the aluminum content is high, together with a high total content of titanium plus aluminum, and formation of eta is enhanced when the titanium content is high, together 'with a high total content titanium plus aluminum. Obviously then it is necessary to limit the titanium to aluminum ratio and total content titanium plus aluminum within those ranges that give maximum effect to the strengthening properties of titanium and aluminum and yet are outside the range where deleterious titanium or aluminum bearing phases occur during solidification or on initial heat treatment.

The titanium and aluminum content also have an indirect effect on formation of deleterious phases such as sigma or mu after prolonged exposures at elevated temperatures. The formation of these phases is enhanced when the total content titanium plus aluminum is high in a high chromium alloy. Therefore consideration must be given to limiting the titanium and aluminum content so as to prevent formation of these phases after prolonged exposure at elevated temperatures as well as to prevent formation of eutectic gamma prime and eta during solidification or on initial heat treatment.

Finally, it is believed that the titanium and aluminum contents have a direct efiect upon sulfidation resistance, in

3 that, high aluminum adversely affects the resistance while titanium enhances such resistance.

The isolife graph in FIG. 1 demonstrates the critical efiect of balancing titanium and aluminum. Existing commercial alloys having similar chemistrics have rupture lives, at comparable test conditions, of 30 to 40 hours. However, by balancing the titanium and aluminum while maintaining other elements also within controlled and critical limits, stress rupture lives of up to 140 hours or more are achieved. To obtain these improved properties, it is necessary to maintain these elements within the area ABCD in FIG. 1. Alloys above line AB have shorter stress rupture life, lower workability and unduly high levels of gamma prime. Alloys to the left of AD have substantially poorer life as shown by the isolife curves. Alloys to the right of BC also have relatively poorer rupture life and lower ductility. Below line CD, alloys have poorer rupture lives and/or are unworkable. The need to observe the limits ABCD is further illustrated by the stress rupture life and ductility data in Table II for compositions listed in Table I.

TABLE I Ratio Heat, Ti Al ('IizAl) Mo Cr Co B l Balance-Nickel.

TABLE II Stress Tensile rupture elong at life room temp., (hrs) percent 2 1,400" F. at 92 k.s.i.

The Larson-Miller diagram in FIG. 2 compares the stress rupture properties of the prior art alloys such as disclosed in US. Pat. 3,385,698 (Example A) and alloys of the invention (Examples B and C). Example A was tested at 1400 E. under a stress of 85 k.s.i. Examples B and C were tested at this temperature but at higher stress levels. The Larson-Miller Parameter enables direct comparison of alloys tested under dilferent stress and tempera ture conditions. The compositions of Example A, B, and C are given in Table 111. It can be seen that the titanium and aluminum balance is critically important in obtaining superior stress rupture life.

1 Balance-Nickel.

It has been found that optimum hot corrosion resistance, strength, creep resistance, and phase stability can be obtained at a ratio of titanium to aluminum of between about 1.75:1 and 3.521 and at a total content of titanium plus aluminum of between about 7.5% and 8.5% when other alloying elements are present in selected amounts.

The chromium content of the invention alloy embraces a range of from about 12% to about 20%. It was found that as chromium is increased the hot corrosion resistance of the alloy is increased and strength is decreased. Conversely, a reduction in chromium results in an increase in strength and a decrease in hot corrosion resistance. The

strength variation is directly related to an increase or decrease in the solvus temperature of gammaprime in gamma as chromium is reduced or increased respectively. Where strength issccondary to hot corrosion resistance, a high chromium content is preferable, and the converse is true when hot corrosion resistance is secondary 'to strength. Preferably, optimum alloy strength and hot corrosion resistance is realized when the chromium content is maintained between about 15% and about 18% and other alloying elements, particularly tungsten, are present in quantities herein stated.

The alloy of this invention contemplates a tungsten content of from about 0.5% to about 2.5%. Tungsten, within specific limits, has been found to increasethe strength of the alloy without enhancing the formation of deleterious phases. Its addition, therefore, overcomes the strength lost either due to a reduction of titanium and aluminum or due to an increase in chromium. The tungsten addition must be closely controlled, however, since it will promote formation of deleterious sigma or mu phases when present in higher percentages in a chromium rich alloy. Optimum characteristics of the invention alloy are obtained when tungsten is maintained within the range of about 1.5% to about 2.0%. The graph in FIG. 3 illustrates the influence of tungsten on rupture life.

The cobalt content of the alloy of the present invention is within the limits of from about 13% to about 19%. In this respect, where strength is the prime consideration, and the additional alloying elements are present in amounts to accomplish this end, the cobalt content is effective for increasing strength proportional to the amount present within the limits stated. Conversely,-where hot corrosion resistance is of primary import, and the additional alloying elements are present in amounts to accomplish this end, no additional strengthening results from increasing amounts of cobalt. Preferably, to optimize strength, hot corrosion resistance, creep resistance and phase stability cobalt is present in the range of from about 13.0% to about 18.0%. The influence of cobalt is graphically shown in FIG. 4. 1

The present invention contemplates a boron addition in the range of from about 0.005% to about 0.03% for the purpose of enhancing both the stress rupture life andthe ductility of the alloy. It was found that .the optimum combination of hot corrosion resistance, strength, creep resistance and phase stability was obtained when boron was present in the amount of from 0.018% to 0.22%

Carbon content of the alloy of this inventionis in the range of from about 0.05% to about 0.15% and has a direct effect upon stress rupture life of the alloy. As carbon increases, stress rupture life also increases, however, such increase in carbon has a concomitant eifect of decreasing the workability of the alloy. Optimum properties appear to occur when carbon lies in the range of 0.05 to 0.12%. The elfect of boron and carbon can be seen by the chart .in FIG. 5.

Molybdenum is present in the invention alloy in quantities of from about 2.0% to about 3.5% and has an effect on alloy strength and workability. It was found, however, that if the molybdenum content goes below 1.5% there is a drastic reduction in alloy strength. Similarly, if the molybdenum content goes above 6.0% it was found that serious workability problems occur as a result of unidentified constituents appearing at the grain boundaries. While the exact limits have not been established, it was determined that molybdenum additions in the range of from about 2.0% to about 3.5% enhanced alloy strength and workability and it appears that optimum properties occur in this range.

Up to 0.75% manganese and/or up to 0.2% yttrium or the rare earths, particularly cerium or lanthanum, may be added to enhance the oxidation resistance of the alloy.

Reference is directed to Table IV which sets forth in tabular form the general and optimum ranges of the alloy of this invention.

TABLE IV Chemical Composition (Percent by Weight) Chromium 1 But Ti:Al ratio must be selected within ABCD of Figure 1. 2 Within ABCD of Figure 1.

The alloy of this invention can be commercially melted by conventional methods and utilized in cast form or hot worked into normal mill products and heat treated to achieve desired mechanical properties. A suitable heat treatment to enhance the properties of the alloy at temperatures up to 1800" F. is as follows:

(1) Heat for 4 hours at 2150 F. (2) Air cool to room temperature. (3) Heat for 4 hours at 1975 F. (4) Air cool to room temperature. (5) Heat for 24 hours at 1550 F. (6) Air cool to room temperature. (7) Heat for hours at 1400 F. (8) Air cool to room temperature.

The alloy of this invention has been successfully formed into about a 40-inch diameter turbine disc by TABLE VI Group I Temp. Stress Liie Elong. R.A. Heat No F.) (k.s.l.) (hrs.) (percent) (percent) 1, 350 90 272. 2 11v 6 14. 5 2735 1, 600 45 129. 9 12. 0 15.1 1, 800 20 49. 2 11.7 13.1 2858 1, 000 45 108. 4 10. 6 15. 8 1, 800 20 57. 2 12. 8 13. 8 350 90 300. 2 10. 9 15. 0 1,600 45 162. 5 7. 8 10. 3 1, 800 20 82. 2 6. 8 10. 5 1, 800 20 70. 3 13. 2 l8. 8 1, 400 92 86. 9 11. 8 l6. 9 l, 400 92 110. 8 11. 1 15. 9

Group II 1, 600 45 54. 8 13. 5 l5. 3 l, 800 20 29. 3 14. 5 13. 4 1, 100 92 69. 6 12. 5 18. 0 2728 1, 800 20 18. 0 l7. 3 16. 0

It is to be noted that the heats in Group I, having chemistries within the invention, have rupture lives markedly greater than those beats in Group II which are essentially identical to comparable heats in Group I except that primarily they are devoid of tungsten and outside the invention.

Typical creep properties of the invention are shown in Table VII showing test results of wrought samples from heat 5167 which were heat treated in the manner hereinbefore detailed and subjected to creep tests.

forging directly from an ingot. In addition the alloy can LE VI] be used for compressor discs or compressor and turbine Tem Stress buckets, and has been successfully formed into both cast m Creep data and forged turbine buckets. Further, the alloy can be used I a for sheet components such as those used autglmerilted 1L5 -ttt hggetgegegt gte1.3353 0 553 5362 thrust applications. For preparation into s eet e a 0y eonga ion 2 v has been subjected to three times the deformation per re L800 iz? 11 igi i $mie i iri i 7 .'6 51 8 315 33221.4 7 heating than weaker alloys outside the scope of the ine1ng&ti11and17-% Rib vention having a nominal chemistry of 15.0% chromium, 18.5% cobalt, 3.3% titanium, 4.3% aluminum, 5.0% molybdenum, 0.06% carbon, 0.02% boron, the balance being nickel.

In addition, the invention alloy can be welded by the In addition to the above properties the alloy of this inert gas process. invention exhibits excellent hot corrosion resistance and For the purpose of giving those skilled in the art a this characteristic is optimized in the alloy class of the inbetter understanding of the invention byway of example vention having the nominal analyses of 18% chromium, a number of alloys of the general compositional range of 15% cobalt, 5% titanium, 2.5% aluminum, 3% molybthe invention were melted and tested. All mechanical test denum, 1.5% tungsten, 0.02% boron, and 0.05% carbon, samples were heat treated as above. Chemical analyses of the balance nickel. representative heats investigated are shown in Table V, Results of sulfidation-erosion tests conducted on samthe Group 1 beats being within the invention and the ples from the invention heats 2814 and 2858 are shown Group II heats being outside the scope of the invention. in FIG. 6 and FIG. 7 compared with various commercial Corresponding stress-rupture test data are shown in hot corrosion alloys having nominal chemistries shown Table VI. in Table VIII.

TABLE v Group I Heat No. Cr Co Ti Al M0 W 0 B N1 TizAl T1+A1 4.93 2.62 2.07 1.5 0.06 0.010 Balance 1.91 7.55 5.0 2.5 3.0 1.5 0.05 a 7.5 4.93 2.5 2.95 1.5 0.07 1. 7.43 5.10 2.19 3.1 1.47 0.07 7.50 6.00 2.44 2.02 1.16 0.11 2. 8.44 0.00 2.42 2.00 1.85011 8.42

Group II 5.10 2.62 3.02 0 0.05 0.020 Balance 1.91 7.78 6.00 2.88 2.01 0 0.11 0.021 r16 2.5;1 8.32 5.06 2.60 3.03 0 0.08 0.018 do 1.911 7.66

TABLE VIII Commercial alloy Cr Ti Al Cb Mo W o 13 Zr Ta Ni A 10.0 10.5 3.0 3.0 4.0 0.00 0.003 Balance. B 15.5 10.0 1.15 4.25 1.75 1.75 3.5 0.15 0.015 .05 c 0.7 0.1 0.34 1.0 1.05 0.05 0.018 0.1 19 D5. D 15.0 18.5 4. 5.0 --000 0.02 Do. E 8.6 10.0 110 6.25 5.0 ..0.13 0.02 0.1 1.5 Do.

FIG. 6 is a plot of sample weight loss versus hours where exposure for invention alloy 2814 as compared to commercial alloys A and D when subjected to both blade cycle and vane cycle su lfidation-erosion tests.

Blade cycle tests consist of heating a blade sample at 1550 F., for three minutes, then to 1850 F., for two minutes and then cooling it to the initial temperature of 1550 F in less than two minutes. This cycle is conducted in an oxidation-sulfidation rig in a media consisting of JPSR combustion products and sea salt. The vane cycle tests are identical to the blade cycle tests except that they are at temperatures 200 F. higher than those shown for the blade cycle. In each test the samples are removed about every 20 hours and Weighed. The weight loss in grams is plotted against total test time in hours.

FIG. 7 shows blade cycle sulfidation-erosion test results for invention alloys 2814 and 2858 as compared with commercial alloys A, B, C, D and E.

An examination of FIG. 6 reveals that the invention alloy 2814 has a weight loss of .75 grams less than commercial alloy A and of 1.5 grams less than commercial alloy D in the blade cycle test and a weight loss of 1.5 grams less than commercial alloy D in the vane cycle test.

An examination of FIG. 7 reveals that invention alloys 2814 and 2858 have a Weight loss ranging from .75 grams to 6.0 grams less than the five commercial hot corrosion alloys used for comparison.

Further, the alloy of the present invention is free of deleterious sigma and mu phases after prolonged periods of exposure at elevated temperatures. Such phase stability was accomplished through utilization of an alloying for mula as follows:

A% =Atomic percent based on the proposition that formation of deleterious sigma and mu phases is a function of the number of electron vacancies (N...) in the bonding orbitals of the elements involved. It was here determined that when N of the residual matrix after precipitation of the hardening phase was equal to or less than 2.38 the alloy was free of sigma and mu phases after exposure under stress at elevated temperatures for prolonged periods of time. The hardening phase is assumed to be na 103 .o2)s

in this calculation. Consequently, each of the heats investigated has an N equal to or less than 2.38 as shown in Table ]X and each is free of deleterious sigma and mu phases when exposed for at least 1500 hours under a stress of 37,000 pounds per square inch at 1500" F.

TABLE IX Heat No. N

Based on the foregoing, it is apparent that the alloy of this invention has an optimum combination of hot corrosion resistance, strength, creep resistance and phase stability.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

What is claimed is:

1. A nickel-base alloy consisting essentially of, by weight, from about 12.0% to about 20.0% chromium, from about 5% to about 7% titanium, from 1.3% to 3.0% aluminum, with the ratio of titanium to aluminum being from about 1.75 :1 to about 3.5:1, and the total content of titanium plus aluminum being from about 6.5% to about 9.0%, from about 13.0% to about 19.0% cobait, from about 2.0% to about 3.5% molybdenum, from about 0.5% to about 2.5% tungsten, from about 0.005% to about 0.03% boron, from about 0.05% to about 0.15% carbon, the balance being essentially nickel with incidental impurities, said alloy being characterized by its freedom from deleterious amounts of sigma and mu 2 phases ensuing from balancing the residual matrix composition to provide an electron vacancy (N value equal to or not greater than 2.38 in accordance with the equation:

2. An alloy according to claim 1 characterized by being free of deleterious phases after exposure for at least 1500 hours under a stress of 37,000 pounds per square inch in the temperature range of 1500 F.

3. An alloy according to claim 1 characterized by a rupture life of at least about 50 hours at 1800 F., under a load of 20,000 pounds per square inch.

4. A nickel-base alloy according to claim 1 having about 15% to about 18% chromium, from about 5% to about 6.5% titanium, from about 2.0% to about 3.0% aluminum, with the ratio of titanium to aluminum being from about 1.75:1 to about 3.5:1 and the total content of titanium plus aluminum being from about 7.5% to about 8.5%, from about 15% to about 18% cobalt, from about 2.5% to about 3.5% molybdenum, from about 1.5% to about 2% tungsten, from about 0.018% to about 0.022% boron, from about 0.05% to about 0.12% carbon, the balance being essentially nickel with incidental impurities.

5. A nickel-base alloy consisting essentially of 15 to 18% chromium, 15% to 18% cobalt, 2.5% to 3.5% molybdenum, 1.5% to 2% tungsten, 0.05% to 0.12% carbon, 0.015% to 0.022% boron, up to 0.5% manganese,

10 up to 0.1% yttrium, up to 0.1% other rare earth elements, References Cited 5 to 6.5% titanium, 2 t0 3% aluminum, the combined P titanium and aluminum content being 7.5% to 8.5% and the titanium to aluminum ratio being within the range 3385698 5/1968 MadFal-lane et 75171 1.75:1 to 3.5 :1, the balance essentially nickel. 5 RICHARD DEAN Primary Examiner 6. A nickel-base alloy according to claim 1 containing up to 0.5% manganese, up to 0.1% yttrium and up to US. Cl. X.-R. 0.1% other rare earth elements. 148-32.5 

